Its autumn here in Sydney Australia. Temps are dropping to below 20C by day 9-12C night. I have 5 Pyrus Calleryana 'Chanticleer' aka Ornamental Pear tree in the front yard, 6 years old 4m tall, never a problem. 4 look healthy and leaves still very green. One tree has ALL its leaves with brown spots and edges and starting to curl up. It started a month ago, but seems to be the whole tree (not one branch or one area/zone) so I suspect its either something systemic (?deficiency) or hopefully this tree has decided to go into autumn much faster than the other 4 (doubt it, they are basically all side by side) It doesn't look like Fire Blight, possibly a rust but the other 4 adjacent trees have no evidence of anything like it. Any suggestion of diagnosis would be really appreciated.
This will be a good news contribution. As far as we know, fireblight is not present in Australia. Fireblight would usually present itself as completely dried out twigs in spring during blossom time and in spots in the tree where it entered, not over the whole tree at the same time unless you missed it a few months ago. Watch carefully as the leaves fall; if they separate normally forming a scar tissue on the twig (if you tug at a leaf it comes away easily) then this is natural abscission (leaf separation) and not disease. Since it is one tree amongst a bunch of them, suspect that the soil at depth is different for that tree and the tree cannot get a particular nutrient; say for example there is bedrock or a layer of pure sand. If it is a nutrient issue then top dressing with well rotted manure of that individual tree might help.
To test for soil quality you can start by driving a long solid rod into the ground and if it suddenly stops several feet down and won't go further you have bedrock. If that is not a problem try driving a long tube (perhaps copper pipe) into the ground and pull a core to get a feel for changing soil conditions.